Hydrogen peroxide, fatty acid

Tryptophan (free and bound in proteins) is a very oxylabile compound, especially in acid solutions. Free tryptophan and tryptophan residues in proteins are oxidised by reactive oxygen species, by hydrogen peroxide, fatty acid hydroperoxides, sulfoxides, perox-yacids and other oxidation agents and can also react via physical quenching, which results in energy transfer and de-excitation of singlet oxygen. 

Hydroxyl tion. Commercial lecithin can be hydroxylated at the unsaturated fatty acid chains by treatment with concentrated hydrogen peroxide and acids like lactic or acetic acid. 

The oxidation of sulfides to sulfoxides and sulfones is achieved in a selective manner using MW irradiation under solvent-free conditions with desired selectivity to either sulfoxides or sulfones over sodium periodate (NaIO4) on silica (20%) (Scheme 8) A noteworthy feature of the protocol is its applicability to long chain fatty sulfides that are insoluble in most solvents and are consequently difficult to oxidize. Further, it circumvents the use of oxidants such as nitric acid, hydrogen peroxide, chromic acid, and peracids, which are conventionally used for the oxidation of sulfides to the corresponding sulfoxides and sulfones. 

Superoxide anion is a relatively nonreactive species in aqueous solution, but in the presence of hydrogen peroxide and a transition metal such as iron, the extremely reactive hydroxyl radical may be generated through a superoxide anion-driven, metal-catalysed Fenton reaction. The hydroxyl radical is able to initiate lipid peroxidation directly through ab.straction of hydrogen from fatty acids leading to the formation of off-flavors and other undesirable compounds. 

Linear alpha-olefins are the source of the largest volume of ahphatic amine oxides. The olefin reacts with hydrogen bromide in the presence of peroxide catalyst, to yield primary alkyl bromide, which then reacts with dimethylamine to yield the corresponding alkyl dimethyl amine. Fatty alcohols and fatty acids are also used to produce amine oxides (Fig. 1). 

The refining process most commonly used involves treatment with hot aqueous alkaH to convert free fatty acids to soaps, followed by bleaching, usually with hydrogen peroxide, although sodium chlorite, sodium hypochlorite, and ozone have also been used. Other techniques include distillation, steam stripping, neutralization by alkaH, Hquid thermal diffusion, and the use of active adsorbents, eg, charcoal and bentonite, and solvent fractionation... 

The mechanism of inhibition by the salts of the long chain fatty acids has been examined . It was concluded that, in the case of the lead salts, metallic lead was first deposited at certain points and that at these points oxygen reduction proceeded more easily, consequently the current density was kept sufficiently high to maintain ferric film formation in addition, any hydrogen peroxide present may assist in keeping the iron ions in the oxide film in the ferric condition, consequently the air-formed film is thickened until it becomes impervious to iron ions. The zinc, calcium and sodium salts are not as efficient inhibitors as the lead salts and recent work has indicated that inhibition is due to the formation of ferric azelate, which repairs weak spots in the air-formed film. This conclusion has been confirmed by the use of C labelled azelaic acid, which was found to be distributed over the surface of the mild steel in a very heterogeneous manner. ... 

These include the mitochondrial respiratory chain, key enzymes in fatty acid and amino acid oxidation, and the citric acid cycle. Reoxidation of the reduced flavin in oxygenases and mixed-function oxidases proceeds by way of formation of the flavin radical and flavin hydroperoxide, with the intermediate generation of superoxide and perhydroxyl radicals and hydrogen peroxide. Because of this, flavin oxidases make a significant contribution to the total oxidant stress of the body. 

Vinyl monomers may be polymerized at favorable rates in an aqueous medium containing an emulsifier and a water-soluble initiator. A typical simple Tecipe would consist of the following ingredients with their proportions indicated in parts by weight 100 of monomer, 180 of water, 2 to 5 of a fatty acid soap, and 0.1 to 0.5 of potassium persulfate. Cationic soaps (e.g., dodecylamine hydrochloride) may be used instead of the fatty acid soap, and various other initiators may replace the persulfate (e.g., hydrogen peroxide and ferrous ion, or a water-soluble organic hydroperoxide). 

It is easier to abstract a hydrogen atom and initiate lipid peroxidation from a fatty acid that has bis-allylic centres than from a fatty-acid side chain with only one double bond. It follows, therefore, that fatty-acid composition should influence the ability of a molecule such as LDL to act as a substrate for peroxidation. The potential... 

Figure 17.2 Lipid peroxidation scheme. LH, a polyunsaturated fatty acid LOOM, lipid hydroperoxide LOH, lipid alcohol L, lipid radical LOO, lipid hydroperoxyl radical LO, lipid alkoxyl radical. Initiation the LH hydrogen is abstracted by reactive oxygen (e.g. lipid alkyl radical, lipid alkoxy radical, lipid hydroperoxyl radical, hydroxy radical, etc.) to produce a new lipid alkyl radical, L. Propagation the lipid alkyl, alkoxyl or hydroperoxyl radical abstracts hydrogen from the neighbouring LH to generate a new L radical.

A large volume (11.25 m3) of mixed fatty acids was to be bleached by treatment with successive portions of 50 wt% hydrogen peroxide. 2-Propanol (450 1) was added to the acids (to improve the mutual solubility of the reactants). The first 20 1 portion of peroxide (at 51°C) was added, followed after 1 min by a second portion. Shortly afterwards an explosion occurred, which was attributed to spontaneous ignition of a 2-propanol vapour-oxygen mixture formed above the surface of the liquid. Oxygen is almost invariably evolved from hydrogen peroxide reactions, and volatile flammable solvents are therefore incompatible components in peroxide systems. 

Where does the hydrogen peroxide originate Many metabolic processes produce hydrogen peroxide as a byproduct. In particular, the degradation of amino acids and fatty acids leads to hydrogen peroxide formation. 

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